Disaccharides When two monosaccharides are covalently bonded together by glycosidic linkages a disaccharide is formed. Glycosidic bond is formed when the hydroxyl group on one of the sugars reacts with the anomeric carbon on the second sugar. Biologically important disaccharides are sucrose, maltose, and Lactose. Maltose Maltose contains two D glucose residues joined by a glycosidic linkage between OH at the first carbon atom of the first glucose residues and OH at the fourth carbon atom of the second glucose forming a α-(1,4) glycosidic linkage as shown in Figure below. Maltose is the major degradative product of Starch.Maltose is hydrolyzed to two molecules of D- glucose by the intestinal enzyme maltase, which is specific for the α- (1, 4) glycosidic bond.
Fig 2.5. Structure of Maltose Lactose Lactose is a disaccharide of β-D galactose and β-D- glucose which are linked by β-(1,4) glycosidic linkage. Lactose acts as a reducing substance since it has a free carbonyl group on the glucose. It is found exclusively in milk of mammals (Milk sugar).
Figure2.6: Structure of Lactose
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